Many vaccines, drugs, foodstuffs and other products are temperature-sensitive, or perishable, and can lose quality with time at rates which are influenced by ambient temperatures. Time-temperature indicators are known which can provide a simple visual indication of the cumulative historical exposure of a host product to heat. The visual indication can be used to provide a signal of when a product may have lost quality, or freshness. Such time-temperature indicators can integrate over time historical temperature exposure to various conditions in a predictable, quantitative manner and can be used to monitor the useful shelf life of perishable host products, or for other purposes.
Known time-temperature indicators can provide a color change at a predetermined end point to indicate possible loss of quality, or freshness, of the host product. The color change can be displayed in a suitable label, or the like, to be read optically, for example, visually by a human viewer. The color change can be chromatic or achromatic or provided by another visually detectable optical parameter change. The temperature-response parameters over time of the time-temperature indicator can be correlated with a deterioration characteristic of the host product to coordinate the color change appropriately with the likely condition of the host product.
Some known time-temperature indicators employ diacetylenic monomer compounds that polymerize in response to environmental conditions such as temperature exposure to provide a color change. See, for example, U.S. Patent Application Publication No. 2009/0131718 by Baughman et al., U.S. patent application Ser. No. 12/730,835 by Castillo-Martinez, U.S. Patent Application Publication No. 2008/0004372 by Prusik et al., U.S. Pat. Nos. 4,789,637 and 4,788,151 to Preziosi et al., and U.S. Pat. Nos. 5,254,473; 5,053,339; 5,045,283; 4,189,399; 4,384,980, and 3,999,946 to Patel.
Some other time-temperature indicators employ diffusion technology, for example, U.S. Pat. No. 6,741,523 to Bommarito, et al.; U.S. Patent Application Publication No. 20030053377 and U.S. Pat. No. 6,614,728, both by and to Spevacek, respectively; and U.S. Pat. No. 5,667,303 to Arens.
Also, certain perishable products, for example, vaccines and sensitive medications, as well as some foodstuffs and other products, including some industrial products can have their quality or safety compromised by relatively brief exposures to a temperature in excess of a predetermined threshold. Various proposals are known for monitoring such temperature exposures, including those in U.S. Pat. No. 7,517,146 to Smith et al. (“Smith et al.” herein), U.S. Pat. No. 5,709,472 to Prusik et al. (“Prusik '472” herein) and its divisional patent, U.S. Pat. No. 6,042,264.
Such known temperature exposure indicators generally appear to be satisfactory for their intended purposes. However, for some purposes there is a need for a time-temperature indicator that has new properties.